/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
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 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent.atomic;

import sun.misc.Unsafe;

/**
 * A {@code boolean} value that may be updated atomically. See the
 * {@link java.util.concurrent.atomic} package specification for
 * description of the properties of atomic variables. An
 * {@code AtomicBoolean} is used in applications such as atomically
 * updated flags, and cannot be used as a replacement for a
 * {@link java.lang.Boolean}.
 *
 * @author Doug Lea
 * @since 1.5
 */
public class AtomicBoolean implements java.io.Serializable {

  private static final long serialVersionUID = 4654671469794556979L;
  // setup to use Unsafe.compareAndSwapInt for updates
  private static final Unsafe unsafe = Unsafe.getUnsafe();
  private static final long valueOffset;

  static {
    try {
      valueOffset = unsafe.objectFieldOffset
          (AtomicBoolean.class.getDeclaredField("value"));
    } catch (Exception ex) {
      throw new Error(ex);
    }
  }

  private volatile int value;

  /**
   * Creates a new {@code AtomicBoolean} with the given initial value.
   *
   * @param initialValue the initial value
   */
  public AtomicBoolean(boolean initialValue) {
    value = initialValue ? 1 : 0;
  }

  /**
   * Creates a new {@code AtomicBoolean} with initial value {@code false}.
   */
  public AtomicBoolean() {
  }

  /**
   * Returns the current value.
   *
   * @return the current value
   */
  public final boolean get() {
    return value != 0;
  }

  /**
   * Atomically sets the value to the given updated value
   * if the current value {@code ==} the expected value.
   *
   * @param expect the expected value
   * @param update the new value
   * @return {@code true} if successful. False return indicates that the actual value was not equal
   * to the expected value.
   */
  public final boolean compareAndSet(boolean expect, boolean update) {
    int e = expect ? 1 : 0;
    int u = update ? 1 : 0;
    return unsafe.compareAndSwapInt(this, valueOffset, e, u);
  }

  /**
   * Atomically sets the value to the given updated value
   * if the current value {@code ==} the expected value.
   *
   * <p><a href="package-summary.html#weakCompareAndSet">May fail
   * spuriously and does not provide ordering guarantees</a>, so is
   * only rarely an appropriate alternative to {@code compareAndSet}.
   *
   * @param expect the expected value
   * @param update the new value
   * @return {@code true} if successful
   */
  public boolean weakCompareAndSet(boolean expect, boolean update) {
    int e = expect ? 1 : 0;
    int u = update ? 1 : 0;
    return unsafe.compareAndSwapInt(this, valueOffset, e, u);
  }

  /**
   * Unconditionally sets to the given value.
   *
   * @param newValue the new value
   */
  public final void set(boolean newValue) {
    value = newValue ? 1 : 0;
  }

  /**
   * Eventually sets to the given value.
   *
   * @param newValue the new value
   * @since 1.6
   */
  public final void lazySet(boolean newValue) {
    int v = newValue ? 1 : 0;
    unsafe.putOrderedInt(this, valueOffset, v);
  }

  /**
   * Atomically sets to the given value and returns the previous value.
   *
   * @param newValue the new value
   * @return the previous value
   */
  public final boolean getAndSet(boolean newValue) {
    boolean prev;
    do {
      prev = get();
    } while (!compareAndSet(prev, newValue));
    return prev;
  }

  /**
   * Returns the String representation of the current value.
   *
   * @return the String representation of the current value
   */
  public String toString() {
    return Boolean.toString(get());
  }

}
